1. Field of the Invention
The embodiments described below relate to a low cost satellite signal demodulator, and more particularly to a low cost satellite signal demodulator that can be configured to sense the presence of a channel and obtain the frequency profile for the channel in a satellite broadcast system in which the channel parameters and the frequency occupancy are not fixed and/or predefined.
2. Background of the Invention
In a satellite television broadcast system, satellites orbiting the earth, receive television programming content from terrestrial transponders and transmit television programming content to terrestrial-based satellite receivers. The receivers receive the signals and pass them to a demodulator circuit typically included in a set up box that is located between the antenna and a television. The demodulator extracts the television programming and makes it available for viewing on the television.
Such satellites are configured to transmit television programming content for a particular satellite television system over a specified frequency spectrum. The frequency spectrum encompasses frequencies within a predefined overall bandwidth (BW), as illustrated in FIG. 1. The overall bandwidth (BW) is typically channelized, i.e., divided into a plurality of channels 102. Each channel 102 is defined by a center frequency (fc) and a channel bandwidth (bw). In many satellite television broadcasting systems, the channel bandwidth (bw) and center frequency (fc) are predefined and information related to these parameters is stored in the set up box. This channel information is then made available to the demodulator so that the demodulator can easily locate and lock on to the center frequency (fc) for a given channel, and can decode information being received over that channel. For efficiency, the channel parameters described above, as well as other parameters such as the symbol rate (SR) and code rate (CR) for each channel, are predetermined and rarely changed. It will be understood, however, that information for many programming channels can be multiplexed onto a single channel.
In certain systems, however, both the channel assignment and the channel parameters can change almost without notice. For example, in certain free-to-air systems, the center frequency (fc) assignment and channel bandwidths (bw) can change. Also, new transponders can appear and the old ones can go off the air. As a result, a conventional set up box demodulator will have difficulty receiving such satellite signals, because the demodulator will often be forced to scan the spectrum bandwidth (BW) in order to detect the channels 102 being used and the associated channel frequency profiles. Conventional demodulators use a time domain, iterative process in order to perform such searching. Unfortunately, such a time domain, iterative process is time-consuming and inefficient. Thus, in systems where the channel assignments and channel parameters are changing often, such time domain, iterative processes can be insufficient.
Thus, set up box manufacturers are essentially forced to design a custom demodulator for a system such as a free-to-air systems, where the channel assignments and parameters change frequently. Designing a custom demodulator, however, can raise costs and reduce manufacturing efficiencies. If the manufacturer does not design a custom demodulator, however, then the demodulator will be inefficient, and consume a prohibitive amount of time for channel scanning when used for systems in which the channel assignments, and channel parameters are not fixed and change often.